The present invention relates generally to the field of electrical safety and, more specifically, to electro-optic control systems which isolate equipment operators from potentially lethal voltages.
There are many circumstances in which electrical isolation of control circuitry is necessary in order to assure personal safety. One outstanding example is the repair of high-tension power lines. Service personnel must often work where power lines are live or where there is some question as to the off-status of a particular line. At the present state-of-the-art a number of lift trucks are available which elevate the operator in a basket in order to put him in close enough proximity to a power line to be able to service it.
The basket itself is often made of a glass fiber compound and an additional insulator is placed between the workbasket and the winched crane assembly. Controls needed to vary the elevation of the workbasket and to control actuators at the base are presently hydraulic. Hydraulic pilot lines are run into the workbasket along with hydraulic controllers. Under ideal conditions the hydraulic lines are almost ideal insulators.
However, hydraulic lines occasionally leak and leave a residue that builds up with time. Carbon bearing deposits contaminate the hydraulic fluid residues leaving a relatively low resistance ground path. At the extremely high voltages encountered in electrical power transmission reaching the lethal current of 100 milliamperes is likely given leakage caused by the contaminated residues. The low resistance leakage path also endangers anyone near the line lift truck itself.